1. Field of the Invention
The present invention relates to a process for producing certain fluorene compounds which are useful as electron-donating coloring agents or chromogenic compounds useful in recording systems particularly recording sheets such as heat-sensitive and pressure-sensitive recording sheets.
2. Description of Related Art
Fluorene compounds useful as chromogenic materials are taught in commonly assigned Japan patent application No. 58-074102 filed Apr. 28, 1983. Continued interest in these compounds is evidenced by the continued research related to these types of compounds (for example recent U.S. Pat. No. 4,658,276) and improvements of processes for their preparation (Japan Kokai No. 61-022076).
In the process for producing a fluorene compound represented by the general formula (II), wherein a lactone compound represented by the general formula (I) is subjected to intramolecular ring closure with a mixture of an anhydrous aluminum halide and a carbonyl compound, generally about 20 hours are required for reaction with some attendant dealkylation noted reducing the quality of the product obtained. In the preferred embodiment herein it was surprisingly found that with addition of a compound having at least one hydroxyl group to the mixture of an anhydrous aluminum halide and a carbonyl compound additional advantages of drastic shortening of reaction time and substantial reduction of dealkylation were obtained.